Waveguide construction



Jan. 1, 1963 H. s. GORDON ETAL 3,070,873

WAVEGUIDE CONSTRUCTION Filed Nov. 1, 1956 4 Sheets-Sheet 1 IEIILEr- EH :EII3. EB

INVENTORS. Hayden .5. Gordon Roy 6. Mar/(er BY Richard E P057 1963 HS. GORDON ETAL 3,070,873

WAVEGUIDE CONSTRUCTION 4 Sheets-Sheet 2 Filed Nov. 1, 1956 I NVENTORS 5. Gordon 6. Marker Hayden Ray R/chard F Jan. 1, 1963 Filed Nov. 1, 1956 H. s. GORDON ETAL I 3,070,873

WAVEGUIDE CONSTRUCTION 4 Sheets-Sheet 4 9.5 l l l yl g5 n 7 040554750 7 MZ/ w & Vl/P/HBLE 96 PEP FREQUENCY r v OWE/Q 0504mm? //v 0/c,4r0/? 1N VENTORS. Hayden S Gordan United States Patent ,070,873 WAVEGUIDE CONSTRUCTION Hayden S. Gordon, Lafayette, Roy C. Marker, Berkeley, and Richard F. Post, Walnut Creek, Calif, assignors to Appiied Radiation Corporation, Walnut Creek, Calif a corporation of California Filed Nov. 1, 1956, Ser. No. 61%,899 18 Claims. (Cl. 29-1555) The present invention relates to electrically resonant mechanical structures in general, and more particularly to an improved method of constructing multiple resonant cavity waveguides and the like.

Transmission characteristics of guiding systems for the propagation of electromagnetic waves are very sensitive to various physical properties established in the particular guiding system, particularly the exact dimensions thereof. It is, therefore, very important that such physical properties in a finished waveguide be precisely determined in the construction thereof for otherwise the characteristics of a system in which the guide is employed would depend upon unpredictable factors which would accordingly render the system inoperable or unreliable. For example, one type of waveguide for use in electron linear accelerators and other devices requiring waveguides for the uniform transmission of radio frequency power compnises a series of coaxially disposed cylindrical cavities coupled one to the other by transverse circular septa having axially aligned apertures or irises provided therein. To insure reliable operation of the finished guiding system the waveguide must be constructed so as to embody certain requisite properties, e.g., the resonant electrical frequency of each cavity must be the same within very close tolerances as determined by the identicalness to very close tolerances of the electrical equivalent volume of each cavity and the diameter and edge-contour of each iris. In addition, each cavity must be spaced at an exact fraction of the wavelength corresponding to the cavity resonant frequency indicating that axial spacing and thickness of the septa must be respectively identical within very close tolerances. It is also desirable that the completed waveguide have low electrical losses, be free of porosity in the cylindrical walls so as to be capable of maintaining a high vacuum in the order of l l() mm. of mercury, and be mechanically sturdy to permit handling and mounting without excessive deflection or destruction of vacuum tightness as well as being capable of being repeatedly heated to temperatures in the order of 600 C. without increasing elecr trical losses, changing the resonant frequency of the cavities, or causing vacuum leaks to develop.

Conventional methods of constructing waveguides of the foregoing type, as well as waveguides of various other designs, have depended upon the most exacting machining operations to establish certain of the above mentioned stringent properties in the finished guide. For example, in waveguides of the type described above the dimensions of the cavity rings and septa including iris apertures are generally carefully machined to mechanical tolerances of at least 10.0001" to establish the desired resonant frequency of each cavity and the axial spacing of the cavities corresponding to an exact fraction of a wavelength. Such finishing machining operations are disadvantageous in that they are difficult, time consuming, and although they establish the above two properties in the waveguide according to mathematical analysis based upon physical dimensions to very close mechanical tolerances, the wave guide does not necessarily conform to desired electrical tolerances. Furthermore, known methods of joining the components of multiple cavity waveguides in the final assembly thereof,

Patented Jan. 1, 1963 e.g., gold diffusion joints, clamping, and the like, are unsatisfactory for establishing mechanical rigidity commensurate with vacuum tightness of the dimensions speci fied above.

The present invention overcomes the disadvantages and limitations associated with known methods of construcing waveguides, and other electrically resonant mechanical structures, as well as furnishing other important advantages by providing an improved method of constructing Waveguides whereby cavity enclosures and septa including inis apertures are separately formed to relatively large mechanical tolerances (e.g.,. $0.001) commensurate with normal machine shop practices. Said enclosures and septa are then each separately checked electrically by appropriate radio frequency means to determine deviations in electrical resonant frequency from a predetermined desired operating resonant frequency after which the dimensions of the enclosures and septa are materially altered by very precisely controlled means to accordingly compensate for such frequency deviations. The enclosures and septa are next oriented and alternately coaxially aligned in final assembled relationship and then rigidly joined by an improved diffusion joining process possessing certain advantages over known assembly methods.

It is, therefore, an object of the present invention to provide an improved method of constructing electrically resonant mechanical structures with great precision.

It is another object of the invention to provide an improved method of permanently tuning resonant cavities with great precision.

It is still another object of the present invention to provide an improved method of constructing mechanical coupling partitions for the transmission of electromagnetic waves possessing electrical resonance characteris tics to very close electrical tolerances.

An important object of the invention is to provide an improved process for joining metallic surfaces with a high degree of rigidity and vacuum tightness.

It is a further object of the invention to provide an improved multiple resonant cavity waveguide having precise and uniform transmission characteristics for the propagation of radio frequency power, and a method of constructing same.

The structure and method of the present invention together with further objects and advantages thereof will be better understood by reference to the following de scription taken in conjunction with the accompanying drawing wherein the structure and method of the invention is described and illustrated with respect to specific steps and apparatus in the interest of clarity, however, no limitations are intended or to be inferred therefrom, reference being made to the appended claims for a precise delineation of the scope of the invention.

In the accompanying drawing: 1

FIGURE 1 is a schematic representation of one embodiment of a finished multiple cavity waveguide;

FIGURE 2 is a cross sectional view of this embodiment taken at 22 of FIGURE 1;

FIGURE 3 is a schematic representationof'a cavity ring of this embodiment formed by conventional manufactuning and machining methods;

FIGURE 4 is a schematic representation of a test fixture for determining the resonant frequency of the vol-' ume enclosed by the ring of FIGURE 3;

FIGURE 5 is a schematic representation of a second test fixture for determining the resonant frequency of the volume enclosed by the ring of FIGURE 3 embodied inan electrical circuit for measuring same;

FIGS. 6A and 6B are a graphical illustration of various oscilloscope patterns obtained by the circuit of FIG- URE 5;

FIGURE 7 illustrates one method of decreasing the volume enclosed by this ring in a controlled manner;

FIGURE 8 illustrates a method of selectively decreasing on increasing the volume enclosed by this ring inva controlled manner;

FIGURE 9 is a schematic representation of a cavity septum of the embodiment illustrated in FIGURE 1 as formed by conventional machining, methods;

FIGURE 10 is a schematic representation of a preferred test fixture and electrical circuit for measuring the resonant frequency of transmission of this septum;

FIGURE 11 illustrates a preferred method of uniformly removing metal from the edge of the center iris of this septum or depositing metal thereon in a precisely controlled manner to tune same to a predetermined operating resonant frequency within very close electrical tolerances;

FIGURE 12 is a schematic representation of a gaging fixture and electrical circuit for determining proper orientations of each septum in the final waveguide assembly; and

FIGURE 13 illustrates an assembly fixture for aligning and clamping rings and septa in final assembled relationship, for purposes of joining and sealing such rings and septa in the final waveguide assembly.

Referring now tothe drawings and FIGURES 1 and 2 in'particular, there is shown a' multiple resonant cavity waveguide structure comprising a plurality of cavity enclosures conventionally formed as coaxial cylindrical cavity rings 11 rigidly attached in pressure sealed relationship to a plurality of correspondingly interposed coaxial transverse circular septa 12, thereby defining a plurality of coaxial spaced resonant cavities 13. Each septum 12 includes a central axial circular iris aperture 14 having rounded edges 16 to provide coupling between adjacent ones of the cavities 13. If will be appreciated that the most sensitive variable affecting the resonant frequency of each one of such cavities 13 is the volume thereof, which is in turn a function of the inner diameter and axial length of the corresponding rings 11 as well as the volume occupied by the adjacent closing-septum 12. Similarly, variations in the diameter of iris apertures 14 and the contour radius of rounded edges 16 thereof affect the resonant frequency of adjacent cavities 13. It is consequently necessary that the foregoing dimensions be held to close tolerances in the manufacture of the finished waveguide.

Proceeding now with a description of an improved method of manufacturing the multiple resonant cavity waveguide illustrated in FIGURE 1, there are first formed a plurality of identical cavity rings 11 (cavity enclosures) which are conventionally cylindrical in cross section as shown in FIGURE 3 although other cross sections are also satisfactory. Rings 11 are fabricated from a good electrically conducting material such as copper and are preferably sawed to approximate length from a tube of appropriate Wall thickness or out upon a lathe, for example,'although said rings may also be formed by other conventional manufacturing processes, e.g., by casting, forging, drawing as cups, or the like.

Rings 11 are next annealed in a hydrogen atmosphere and machined to close tolerances in theorder of $0.001

commensurate with standard machine-shoppractices as by turning the outside ring diameter on a lathe or a centerless grinder, reaming or boring the inside ring diameter, and facing or grinding the transverse end extremities to appropriate axial length. After machining, both end extremities of each ring 11 are lapped flat and smooth to insure very accurate fits in the finished waveguide, and this may be accomplished by rotating a flat surface in intimate contact with said end extremities, preferably in a liquid or paste form. I

Each cavity ring 11 is nextplaced in a suitable test fixture for gaging the electrical resonant frequency thereof. One such fixture 17 as illustrated in FIGURE 4 comprises a pair of flat electrically conducting plates l8, 19 adapted to be disposed in closing relationship at the end extremities of ring 11 to form an enclosed cavity 21. One plate 19 is fitted with conventional excitation and pickup loop connectors 22, 23 respectively terminating in input and output coaxial cables, 24, 26 to admit and extract 32 provided therein and at the other end extremity to a standard septum 33 including a central axial reference iris aperture 34 thereby forming a standard cavity 35. Said cavity element 28 is disposed in closing relationship at septum 33 wtih one end extremity of cavity ring 11, the other end extremity of which is closed by an end plate 36 provided with a central axial half iris 37 thereby describing an enclosed cavity 38 coupled through iris 34 to standard cavity 35. Plate 36 is fitted with conventional excitation and pick-up loop connectors 39, 41 respectively terminating in input and output coaxial cables 42, 43 to admit and extract electrical energy from coupled cavities 33, 35. Fixture 27 thus provides means for gaging cavity rings 11 in the same electrical mode as is established in the finished waveguide assembly, i.e., in the mode established in two adjacent cavities 35, 38 coupled by an iris 34.

. conjunction with an abrasive compound rn, for example,

In order to determine the resonant frequency of each cavity ring 11, test fixture 17 or test fixture 27 is con nected in a measuring circuit as illustrated in FIGURE 5 (fixture 27 is shown connected in the circuit of FIGURE 5 at cables 42, 43 although fixture 17 may be similarly connected at cables 24, 26). As shown in the foregoing figure, coupled cavities 38, 35 are excited by connecting input cable 42 to the output of a swept oscillator 44 which is frequency modulated at 60 cps. by a sweep voltage supply 46. A swept oscillator as herein utilized is conventionally defined as a radio frequency oscillator which is frequency modulated by a relatively low modulating frequency to produce a relatively large frequency deviation, i.e., the generated output voltage of oscillator 44 as ap plied to cavities 38, 35 varies back and forth over a band. of frequencies.

Electrical energy from cavities 38, 35 is extracted and": applied by output cable 43 to the input of a voltage de-- tector 47. The extracted energy is also applied by means of a T-section 48 in cable 43 through an adjustable attenu-- dent upon the calibrated frequency setting of cavity 51.. The output of voltage detector 47, i.e., a voltage signal proportional to the energy extracted from cavities 38, 35' diminished by the energy absorbed by reference cavity 51 as a function of frequency, is applied to vertical deflection plates 52 of a cathode ray oscilloscope 53. The horizontal deflection plates 54 of such oscilloscope are connected to the output of sweep voltage supply 46 to provide a horizontal deflection of the oscilloscope beam which is synchronized to the frequency change of the detector output signal applied to vertical deflection plates 52. The oscilloscopic display produced at the viewing screen of oscilloscope 53 is consequently a visual indication of the change in power transmission through cavity 38 enclosed by ring 11 with respect to frequency as illustrated graphically in FIGURE 6A. It is to .be noted that such display includes a reference pip 56 due to the energy absorbed by reference cavity 51 .and therefore corresponding to the calibrated frequency setting thereof. Cavity 51 may consequently be tuned until pip 56 coincides with the resonant peak of the oscilloscopic display as illustrated graphically in FIGURE 6B, the calibrated frequency setting of cavity 51 being then equal to the resonant frequency of cavity ring 11.

At this point it should be noted that the configurations of the test fixtures 17, 27 and circuit utilized for resonant frequency measurements in the method of the present invention are not limited to the embodiments illustrated in FIGURES 4 and 5 and hereinbefore described, as numerous other satisfactory resonant frequency measuring means exist which are well known to persons skilled in the electronic art.

In order that all cavity rings 11 possess the same predetermined operating resonant frequency in the finished waveguide within very close electrical tolerances, those cavity rings having resonant frequencies as determined above different from such operating frequency must be accordingly compensated. Since the resonant frequency of a cavity varies inversely with the volume thereof, the volumes enclosed by those cavity rings 11 having a measured resonant frequency less than the predetermined operating resonant frequency must be decreased in a precisely controlled manner to tune the cavity resonant frequency to operating frequency within very close electrical tolerances. Similarly the volumes of undersized cavity rings 11 having two great a resonant frequency must be increased in a controlled manner to tune same substantially precisely to the standard predetermined operating frequency.

Tuning of oversized cavity rings 11 (i.e., cavity rings 11 enclosing too great a volume) may best be accomplished by brinelling, i.e., by pressing local indentations 57 in the shape of shallow spherical segments into the peripheral wall surfaces of rings 11 to produce corresponding bulges at the interior wall surfaces of such ring extending into the enclosed cavity volume as shown in FIGURE 7. Indentations 57 are preferably effected by a single indenting punch 58 or annular array thereof pressed radially inward into the outer periphery of rings 11, each punch 58 having a restricting collar 59 to limit depth of penetration and adapted to engage a semispherical forming die 61 at the interior Wall surfaces of ring 11 such that all indentations 57 are of substantially identical size. Each indentation 57 produces a small, distinct and consistent change in the cavity volume enclosed by rings 11 sufficient to produce a change in resonant frequency corresponding to an acceptable frequency tolerance. Consequently, to tune an oversized cavity ring 11 having a known frequency deviation from operating resonant frequency, it is only necessary to indent such ring a predetermined number of times as calculated by dividing the total frequency deviation by the frequency change per indentation. The indentations 57 may or may not be symmetrically disposed and may or may not be of an even number depending on the magnitude of perturbations of the electric field allowable within the cavity enclosed by the ring 11. In addition the effect of slight out-of-roundness in the cavity rings 11 produced by indentations 57 has been shown not to affect frequency measurement. Furthermo-re, it has been observed in practice that frequency tolerance of substantially any shaped resonant cavity can be easily held to 1 part in 30,000 or more by the foregoing indentation tuning operation without requiring a corresponding increase in the machining accuracy of the cavity enclosure dimensions thereby resulting in the important advantage that the tuning of resonant cavities may be precisely performed by persons unskilled in electric or metal working arts.

The volum enclosed by oversized cavity rings 11 may also be uniformly decreased in a controlled manner by depositing additional metal in controlled amounts on the interior wall surfaces of such rings by means of electroplating as shown in FIGURE 7. The cavity rings 11 are suspended in a tank 62 containing a suitable electrolyte 63 (plating bath). An elongated electrode 64 fabricated for example from copper isalso suspended within tank 62 concentric with reference to ring 11. Electrode .64 and ring it are connected in series with a battery 66 through a switch 67. With switch 76 closed a uniform metallic layer is plated upon the interior wall surfaces of ring 11 in a well known manner. Since electroplating deposits the metallic layer upon the interior wall surfaces of cavity rings 11 at a very slow rate, the increase in resonant frequency accordingly produced by the decrease in cavity volume is easily controllable within limits of 1 part in 30,000 or more by varying the time or current, or both. After electroplating the oversized cavity rings 11 in the foregoing manner, the resonant frequency of such rings is again measured as by the gaging means illustrated in FIGURE 5 to determine any remaining deviations from operating resonant frequency. Such electroplating and measuring process is continued until the resonant frequency of the cavity ring 11 agrees with operating resonant frequency.

Tuning of undersized cavity rings 11 (i.e., cavity rings 11 enclosing too small a volume) is preferably accomplished by increasing the volum enclosed by such rings in a controlled manner as by means of electropolishing the interior wall surfaces thereof. Since electropolishing is the reverse process of electroplating as illustrated in the embodiment of FIGURE 8, such electropolishing may best be accomplished in a similar manner with the battery polarity reversed and plating bath electrolyte 63 replaced by a suitable polishing bath. Since electropolishing removes metal at a very slow rate, just as electroplating deposits metal at a very slow rate, the decrease in resonant frequency accordingly produced by the increase in cavity volume is easily controllable within limits of 1 part in 30,000 or more by appropriately varying the time or current or both.

The plurality of identical septa 12 are next formed in the improved method of manufacturing waveguides of the character illustrated in FIGURE 1. Such septa 12 conform to the particular cross section of the cavity rings 11 utilized in the waveguid construction and are therefore conventionally formed as circular discs having a diameter substantially identical to the outside diameter of cavity rings 11 as shown in FIGURE 8. Each septum 12 includes a central iris aperture 14 having rounded edges 16, which aperture is conventionally circular in waveguides of circular cross section although it is sometimes desirable that said apertures be rectangular or of various other configurations.

Septa 12 are fabricated from a good electrically conducting material and are therefore preferably cut from copper plate or bar stock of appropriate size and cross section followed by drilling of apertures 14, although said septum may also be formed by other well known manufacturing processes, e.g., by casting, forging, or punching and blanking.

Septa 12 are next annealed in a hydrogen atmosphere to remove internal stresses and strains established therein due to the foregoing cold forming operations. The diameter and thickness of septa 12, diameter and rounded edges 16 of iris apertures 14, are then machined to close tolerances in the order of $0.001" commensurate with standard machine shop practices as by turning the septum diameter to the outside diameter of cavity rings 11 on a lathe or centeriess grinder, turning the aperture diameter and forming rounded edges 16 on aisle, and facing or grinding the septa end faces to suitable thicknesses. After the above machining operations the septum end faces are lapped flat and smooth to insure very accurate fits in the finished waveguide, and this may be accomplished by rotating a fiat surface in intimate contact with said end faces, preferably in conjunction with an abrasive compound in, for example, a liquid or paste form.

Each septum 12 is next gaged electrically to determine deviations in the transmissive resonant frequency of iris apertures 14 from the hereinbefore mentioned predeten mined waveguide operating resonant frequency in a manner similar to that previously described in relation to cavity rings 11. Said gaging may be best accomplished by placing each septum 12 in a gaging fixture 68 as illustrated in FIGURE 10. As shown therein, fixture 68 comprises a pair of standard cavity rings 69 having said predetermined operating frequency one disposed coaxially adjacent each end face of a septum 12 to be tested. Standard electrically conducting end plates 71, 72 each provided with a central axial half iris 73 are respectively disposed in closing relationship at the open end extremities of rings 69 to form a pair of coaxially adjacent resonant cavities 74 coupled by means of the test septa iris aperture 14 thus simulating the finished waveguide structure, and the entire fixture assembly so formed is rigidly clamped under axial force as shown generally at '76. One plate 72 is fitted with conventional excitation and pickup loop connectors 77, 78 respectively terminating in input and output coaxial cables 79, 81 to admit and extract electrical energy from the axially coupled cavities 74.

Deviations in the transmissive resonant frequency of iris aperture 14 of test septum 12 from standard operating resonant frequency may be determined by numerous methods familiar to persons skilled in the electronics art, e.g., by means of the measuring circuit as illustrated for the sake of simplicity in FIGURE wherein gaging fixture 68 is excited by a calibrated variable frequency oscillator 82 coupled to input coaxial cable 79 and the response of said fixture is observed at a suitable radio frequency power indicator 83 (e.g., a crystal detector, bolometer, or simple radio receiver) connected to output coaxial cable 81.

The measuring procedure then consists in varying the frequency of oscillator 32 and observing the calibrated frequency setting at which indicator 83 indicates maximum response of fixture 68. Greater accuracy may be obtained however by considering the resonant frequency to be the mean of two frequencies on either side of resonance at which the indicated response is less than at resonance by some specified amount such as 3 decibels.

Septa 12 having resonant frequencies deviating from operating resonant frequency as indicated by the foregoing measuring procedure must be accordingly compensated. Septa having too small or too great an associated resonant frequency respectively indicating undersized and oversized diameters of iris apertures 14 may be accordingly tuned to operating resonant frequency within very close electrical tolerances by removing or depositing small controlled amounts of metal uniformly at rounded edges 16 thereof preferably by means of electropolishing or electroplating followed by electropolishing.

Undersized septa iris apertures may best be electropolished as illustrated in FIGURE 11. Each septum 12 is rigidly interposed between two annular thief electrodes 84 disposed coaxial with reference to iris aperture 14 and having inner wall surfaces intersecting rounded edges 16 circumferentially. The resulting assembly is suspended in a tank 86 containing an electrolyte 87, suitable for electropolishing (i.e., a polishing bath). An elongated cylindrical electrode 88 having a reduced center section 39 and conventionally fabricated from the same material as septa 12 is suspended coaxially symmetrical within the submerged septum 12 and thief electrode assembly. Electrode 88 is singly connected and one thief electrode 84 and septum 12 are commonly connected in series with a battery 91 through a switch 92. With switch 92 closed, metal is uniformly removed from the rounded edges 16 of aperture 14 by electrolysis; removal of metal from the remaining portions of septum 12 being prohibited by the shielding effects of thief electrodes 84. As was previously mentioned in regard to electropolishing of the interior wall surfaces of cavity rings 11, such electropolishing process removes metal at a very slow rate. Consequently the increase in size of aperture 14 and therefore the corresponding increase in associated resonant frequency is easily controllable within limits of 8 1 part in 30,000 or more by varying the time and/or current employed in the electropolishing process.

Electroplating of the rounded edges 16 of oversized apertures 14 is similarly employed to decrease the resonant frequency thereof in proportion to the amount of metal deposited by utilizing electrolysis structure similar to that illustrated in FIGURE 11 and described above in regard to electropolishing but wherein electrolyte 87 is suitable for plating (i.e., a plating bath) and the polarity of battery 91 is reversed. The same degree of control of resonant frequency change is possible with electroplating as with electropolishing (i.e., 1 part in 30,000 or more) by varying the time and/or current employed in the plating process. It is advantageous to plate suflicient metal upon edges 16 of oversized iris apertures 14 to decrease the resonant frequency thereof below operating resonant frequency such that electropolishing of rounded edges 16 may be finally employed to precisely tune said septa to operating resonant frequency. Electropolishing, in addition to providing a means of precisely tuning septa 12 to operating resonant frequency, produces a high degree of smoothness upon aperture rounded edges 16 thus minimizing voltage breakdown between adjacent septa in the finished waveguide assembly.

After electropolishing septa 12, the resonant frequency thereof is again measured as by means of the gaging fixture 63 and measuring circuit illustrated in FIGURE 10 to determine any remaining deviations from operating resonant frequency and such deviations are appropriately compensated for by further electropolishing or electroplating followed by electropolishing until subsequent measuring indicates resonant frequencies in agreement with operating resonant frequency.

Since the resonant frequency of the cavities formed by cavity rings 11 interposed between transversely disposed septa 12, although tuned to a common operating resonant frequency as hereinbefore described, is affected by the flatness of the faces of said septa, appropriate orientation of each septum 12 in the final waveguide assembly is next determined to minimize differences in resonant frequency between adjacent cavities. The foregoing is best accomplished by placing each septum 12 in a test fixture 93 as shown in FIGURE 12. Fixture 93 comprises a non-resonant cavity enclosure 94 disposed coaxially adjacent one end face of a septum 12 to be oriented forming a non-resonant cavity 96 therewith, and a standard cavity ring 97 (i.e., having a resonant frequency equal to operating resonant frequency) coaxially disposed between the other end face of said septum and a standard transverse end plate 98 thereby forming a resonant cavity 99. The entire fixture assembly 93 is clamped under axial force as shown generally at 101 and end plate 98 is provided with conventional excitation and pickup loop connectors 102, 103 respectively terminating in input and output coaxial cables 104, 106. A calibrated variable frequency oscillator 107 is connected to input cable 104 to excite cavity 99 and the response thereof is observed at a suitable radio frequency power indicator 108 (e.g., a crystal detector, bolometer, or simple radio receiver) connected to output coaxial cable 106. The frequency of oscillator 107 is then varied and the calibrated frequency setting is observed at resonance which corresponds to maximum response of fixture 93 as indicated by indicator 108. Since the frequency of a resonant cavity coupled to a non-resonant cavity is very sensitive to the flatness of the coupling septum, the resonant frequency of cavity 99 is measured with septum 12 oriented first with one end face and then the other end face adjacent cavity 96. The out-of-fiatness of septa 12 being essentially conical in nature, i.e., septa 12 are minutely deformed into cones truncated at iris apertures 14, results in cavity 99 having slightly less volume at one orientation of said septa than at the other. The corresponding measured resonant frequencies of cavity 99 consequently difler slightly for each orientation of septum 12. For example, the calibrated frequency setting of oscillator 107 at resonance may be 300 me. for one end face of a particular septum 12 adjacent cavity 99 while being 300.1 rnc. for the other end face of said septum adjacent cavity 99. Since the out-of-latness of each septum 12 (i.e., the taper of the minute conical deformations) should be in the same direction in the finished waveguide assembly to minimize differeuces between the resonant frequencies of adjacent cavities, the direction of out-of-flatness of each septum 12 is accordingly noted as by marking the periphery thereof with a small notch at the end face producing, for example, the highest observed resonant frequency.

With all cavity rings 11 and septa 12 tuned to the same predetermined operating resonant frequency and a common orientation of said septa noted, said rings and septa are coaxially aligned in final waveguide assembly relationship as by alternately placing rings and septa upon V-blocks or parallel bars, septa 12 being oriented with marked end faces facing the same axial direction. The cavity rings 11 and septa 12 are next axially compressed as by means of a clamping fixture 109 adapted to exert uniform pressure axially inward as shown in FIGURE 13.

Clamping fixture 109 is fabricated entirely from heat resistant alloy such as stainless steel and comprises an elongated tie rod 111 threaded at both end extremities which is inserted through the axially aligned iris apertures 14 of septa 12. Cylindrical intermediate plates 112, 113 respectively having annular peripheral shoulders 114, 116 and 117, 118 in each end face thereof and central axial bores 119, 121 engaging tie rod 111 are respectively disposed adjacent the end extremities of the waveguide assembly. The end faces of the end cavity rings 11 respectively interlock with shoulders 116, 118 while cylindrical end plates 122, 123 having central axial bores 124, 126 respectively engaging tie rod 111 are provided with annular axially projecting rims 127, 128 respectively bearing against intermediate plate shoulders 114, 117. A cylindrical compression equalizer plate 129 including a central axial bore 131 engaging tie rod 111 is disposed coaxially adjacent end plate 123 and nuts 132, 133 are threadably secured to the end extremities of tie rod 111 and cinched tight against end plate 122 and equalizer plate 129 respectively. To insure that such compression is uniform over the entire mating surface area of each adjacent pair of rings 11 and septa 12, a plurality of annularly spaced back-off bolts 134 are provided in equalizer plate 129 extending through threaded bores 136 to bear against end plate 123 at points axially aligned with the end faces of cavity rings 11. Bolts 134 are appropriately tightened to accordingly back-off equalizer plate 129 until the axial spacing of same from end plate 123 is circumferentially uniform as indicated for example by a plurality of identical circumferentially spaced micrometer readings thereby indicating uniform axial compressron.

The clamped cavity rings 11 and septa 12 are now integrally joined together to form the finished waveguide and this may be best accomplished by diffusion welding the mating surfaces of said rings and septum followed by brazing of the welded joints to provide vacuum tightness. The foregoing joining process is accomplished by first placing a suitable brazing alloy 137 (e.g., in the case of copper rings and septum solder of composition 72% Ag28% Cu) in intimate contact with each juncture of the clamped cavity rings 11 and septa 12. Such brazing alloy 137 may be applied in paste form, as power combined with a suitable binder, or as foil or ribbon tied about or preformed into rings slipped over said junctures as illustrated in FIGURE 13. The clamped assembly including brazing alloy 137 is next placed in a reducing atmosphere, such as hydrogen or forming gas (i.e., 95% N H to prevent oxides from forming on the surfaces to be joined and heated to 450 C.600 C. for several hours thus causing diffusion to occur between the contacting surfaces of cavity rings 11 and septa 12 and in effect welding same together into one mass. It has been illustrated in practice that such diffusion welded joints possess excellent electrical properties and mechanical strength, however, they are porous to high vacuum. Consequently, upon completion of the diffusion process, the temperature of the waveguide assembly is raised to melt the brazing alloy 137 which in turn flows to seal each joint vacuum-tight. After the solder has flowed, the assembly is cooled and removed from clamping fixture 109 thus resulting in the finished multiple resonant cavity waveguide assembly.

It will be appreciated that various other methods exist for joining the cavity rings 11 and septum 12 into an integral waveguide assembly, however, such methods are variously disadvantageous. For example, diffusion joints between adjacent cavity rings 11 and septum 12 may be obtained by utilizing a noble metal such as gold in the form of electroplated layers upon the surfaces to be joined and applying heat and/or pressure thereto; such noble metal maintaining oxide-free surfaces while being heated. The previously described diffusion joining method is consequently preferred in that the tedious, more expensive, electroplating of noble metal upon the surfaces to be joined in the latter process is eliminated.

There has been described hereinbefore an improved method of constructing waveguides and the like which has been illustrated and described in connection with but some of many possible embodiments and with respect to specific steps and structure, however same are presented as illustrative only of certain embodiments of the invention. Another example of structure to which the hereinbefore described precision method of constructing electrically resonant cavities and coupling partitions for the transmission of radio frequency power may be advantageously applied is a waveguide buncher assembly comprising a plurality of axially aligned cavity rings and coupling septa constructed in such manner that the said cavities possess different predetermined resonant frequencies and radio frequency transmission characteristics which vary uniformly from cavity to cavity along the axis. The foregoing illustrations are to be taken only as examples and in no way limiting the scope of the invention which is precisely delineated in the following claims.

What is claimed is:

1. A method of producing a multiple cavity waveguide comprising the steps of 1) forming from electrically conducting material a plurality of similar enclosures having open ends and a plurality of flat septa conforming to the exterior cross section of said open ends and having central iris apertures therethrough, (2) electrically testing each of said enclosures to determine the resonant frequency thereof, (3) comparing said resonant frequencies to a predetermined operating resonant frequency to determine deviations therefrom, (4) altering the interior volume of said enclosure as required to produce resonance thereof at said operating frequency, (5) repeating steps (2), (3), and (4) alternately until said enclosures resonate at said operating frequency, (6) electrically testing the iris apertures of each septum to determine the transmissive resonant frequency thereof, (7) comparing said transmissive resonant frequency to said operating frequency to determine deviations therefrom, (8) altering the size of said apertures as required to produce resonance thereof at said operating frequency, (9) repeating steps (6), (7), and (8) alternately until said septa apertures resonate at said operating frequency, (10) determining the axial direction of out-of-fiatness deformation of each one of said septa, and (11) assembling said enclosures and said septa all oriented in the same direction of out-of-flatness in alternate coaxial relationship.

2. The method defined by claim 1 further defined by step (4) consisting in controllably indenting the walls of said enclosures determined to deviate below said operating frequency from the exterior to precisely reduce the internal volumes of said enclosures and provide a resonant frequency thereof equal to said operating frequency, and electropolishing the walls of said enclosures determined to deviate above said operating frequency to uniformly remove metal therefrom in controlled amounts thereby precisely increasing the internal volumes of said enclosures and providing a resonant frequency thereof equal to said operating frequency.

3. The method defined by claim 1 further defined by step (8) consisting in electropolishing the edge surfaces of septa iris apertures determined to produce transmissive resonant frequencies deviating below said operating frequency whereby metal is uniformly removed from said surfaces in precisely controlled amounts to tune said apertures to said operating frequency Within close electrical tolerances, and electroplating the edge surfaces of septa iris apertures determined to produce transmissive resonant frequencies deviating above said operating frequency whereby metal is uniformly deposited upon said surfaces in precisely controlled amounts to tune said apertures to said operating frequency within close electrical tolerances.

' 4. In the manufacture of multiple cavity waveguides formed of a plurality of cavity enclosures and interposed septa having axial iris apertures provided therein, the method consisting of (1) individually electrically comparing the resonant frequency of said enclosures with a predetermined operating resonant frequency, (2) controllably impressing identical local indentations into the periphery of enclosures having resonant frequencies less than said operating frequency to form correspond ing bulges at the interior wall surfaces thereof, (3) repeating steps (1) and (2) alternately until said enclosures resonate at said operating frequency, (4) electropolishing the interior walls of enclosures having resonant frequencies greater than said operating frequency, (5) repeatiug steps (1) and (4) alternately until the resonant frequency of said enclosures is -in agreement with said operating frequency, (6) electrically comparing the resonant frequency of transmission of said septa iris apertures to said operating frequency, (7) electropolishing the edge surfaces of septa apertures having resonant frequencies less than said operating frequency, (8) repeating steps (6) and (7) alternately until the resonant frequency of said septa apertures is equal to said operating frequency, (9) electroplating the edge surfaces of septa apertures having resonant frequencies greater than said operating frequency, (10) repeating steps (6) and (9) alternately until the resonant frequency of said septa apertures is less than said operating frequency followed by step (8), (11) determining the axial direction of outof-flatness deformation of each one of said septa, (12) placing said enclosures and said septa in alternate coaxial juxtaposition, (13) orienting said septa inthe same direction of out-of-flatness, (14) axially clamping said enclosures and septa, (15) diffusion welding together said clamped en :losures and septa to obtain diffusion welded joints therebetween, said diffusion welded joints being porous to vacuum, (16) brazing the porous diffusion welded septum-enclosure joints to vacuum seal the same, and (17) unclamping said joined septa and enclosures.

5. A method of producing a multiple cavity waveguide having a plurality of axially aligned open ended cavity enclosures separated by centrally apertured transverse septa comprising the steps of (1) forming from electrically conducting material a plurality of similar enclosures and flat septa with central apertures therethrough, (2) closing each of said enclosures and energizing the interior volume thereof with a radio frequency field, (3) varying the frequency of said field simultaneously while observing the frequency response of said enclosures, (4) noting the frequency producing peak response, (5) comparing said frequency to a predetermined operating frequency, (6) altering the interior volume of said enclosures as required to produce peak response at said operating frequency, (7) interposing each one of said septa be-' tween identical cavity enclosures resonate at said operating frequency, (8) energizing the interior of said cavity enclosures with a radio frequency field, (9) repeating steps (3), (4), (5), (l0) altering the size of saidsepta iris apertures as required to produce peak response at said operating frequency, (11) interposing each one of said septa between a non-resonant cavity enclosure and a cavity enclosure resonant at said operating frequency, 12) energizing the interior of said cavity enclosures with a radio frequency field, (l3) repeating steps (3) and (4), 14) rotating each of said septa transversely upside down and repeating steps (l1), (l2), and (13), (15) marking the septum end face noted to produce peak response at greatest frequency, (16) and assembling said enclosures and septa in alternate coaxial relation ship, said septa marked end faces oriented in the same axial direction.

6. A method as defined by claim 5 further characterized by step 10 consisting in electroplating the edge surfaces of septa iris apertures producing peak response at frequencies greater than said operating frequency, repeating steps (7), (8), (9) alternately with the foregoing step until peak response is produced at a frequency less than said operating frequency, electropolishing the edge surfaces of septa iris apertures producing peak response at frequencies less than said operating frequency, and repeating steps (7), (8), (9) alternately with the immediately preceding step until peak response is produced at said operating frequency.

7. A method as defined by claim 5 further characterized by step (6) comprising electroplating the inner wall surfaces of enclosures producing peak response at frequencies less than said operating frequency, repeating steps (2), (3), (4), (5) alternately with the immediately preceding step until peak response is produced at said operating frequency, electropolishing the inner wall surfaces of enclosures producing peak response at frequencies greater than said operating frequency, and repeating steps (2), (3), (4), (5) alternately with the immediately preceding step until peak response is produced at said operating frequency. 8. A method as defined by claim 5 further defined by step (6) consisting in controllably impressing identical local indentations into the periphery of enclosures producing peak response at frequencies less than said operating frequency to form corresponding bulges at the interior wall surfaces thereof, repeating steps (2), (3), (4), (5) alternately with the foregoing step until peak response is produced at said operating frequency, electropolishing the interior wall surfaces of enclosures producing peak response at frequencies greater than said operating frequency, and repeating steps (2), (3), (4), (5') alternately with the foregoing step until peak response is produced at said operating frequency.

9. In the manufacture of multiple cavity waveguides formed of a plurality of cavity enclosures and interposed septa having axial iris apertures provided therein, the method consisting in closing each one of said enclosures and energizing same with a variable radio frequency field simultaneously while observing the frequency response of said enclosure to determine the frequency at which peak response occurs, comparing the resonant frequencies so determined to a predetermined operating resonant frequency and determining deviations therefrom, electropolishing the interior Wall surfaces of enclosures deviating above said operating frequency to produce a change in resonant frequency compensatory to the deviation, controllably indenting the Walls of enclosures deviating below said operating frequency from the exterior as required to produce a change in resonant frequency compensatory to the deviation, interposing each septum between identical cavities resonant at said operating frequency, energizing said septum coupled cavities with a variable radio frequency field simultaneously while observing the frequency response of said cavities to determine the frequency at which peak response occurs, comparing the septa aperture resonant frequencies so determined to said operating resonant frequency and determining deviations therefrom, selectively electroplating and electropolishing the aperture edge surfaces of septa deviating from said operating frequency to produce corresponding changes in resonant frequency compensatory to the deviations, interposing each septum between a cavity resonant at said operating frequency and a non-resonant cavity, energizing said cavities with a variable radio frequency field while observing the frequency response of said cavities to determine the frequency producing peak response, orienting said septum transversely upside down between said cavities and repeating the immediately preceding step, marking the septum end face orientation producing peak response at greatest frequency, and assembling said enclosures and septa similarly oriented with reference to the end faces thereof in rigid pressure sealed alternate coaxial relationship.

10. A method of manufacturing multiple cavity waveguides comprising the steps of (1) providing a plurality of cavity enclosures having open ends, (2) providing a plurality of septa conforming to said open ends and each including a central axial aperture, (3) machining the length and outer periphery of said enclosures respeztively identical within close tolerances, (4) machining the interior dimensions of each of said enclosures to predetermined dimensions commensurate with a predetermined operating frequency within close tolerances greater than said predetermined dimensions, (5) machining the periphery of said septato conform to the outer periphery of said enclosures within close tolerances, (6) machining the dimensions of each of said septa apertures to predetermined dimensions commensurate with said operating resonant frequency within close tolerances less than said predetermined dimensions, (7) annealing said enclosures and septa in a reducing atmosphere, honing the transverse faces of said enclosures and said septa flat and smooth, (8) closing each one of said enclosures and energizing same with a variable radio frequency field simultaneously while observing the frequency response of said enclosure to determine the frequency at which peak response occurs, (9) comparing the resonant frequencies so determined to said operating resonant frequency to determine deviations therefrom, (l0) decreasing the internal volume of each enclosure, (11) repeating steps (8) and (9) alternately with step until the resonant frequency of said enclosure is equal to said operating frequency, (12) interposing each septum between identical resonant cavities having said operating resonant frequency, (13) energizing said septum coupled cavities with a variable radio frequency field simultaneously while observing the frequency response of said cavities to determine the frequency at which peak response occurs, (14) comparing the septa resonant frequencies so determined to said operating resonant frequency and determining deviations therefrom, 15) increasing the aperture size of each septum, (16) repeating steps (12), (13), (14) alternately with step (15) until the resonant frequency of said septum is equal to said operating frequency, (17) interposing each septum between a cavity resonant at said operating frequency and a non-resonant cavity, (18) energizing said cavities with a variable radio frequency field while observing the frequency response of said cavities to determine the frequency producing peak response, (19) orienting said septum transversely upside down and repeating steps 17) and (18), (20) marking the septum end face orientation producing peak response at greatest frequency, and (21) and assembling said enclosures and septa similarly oriented with reference to the marked end faces thereof in rigid pressure sealed alternate coaxial relationship.

11. A method as defined by claim 10 further characterized by step (10) consisting in electroplating theinterior wall surface of each enclosure to uniformly deposit metal thereon in controlled amounts and thereby precisely decrease the internal volume of said enclosure, and step (15) consisting in electropolishing .the aperture edge surface of each septum to uniformly remove metal therefrom in controlled amounts and thereby precisely increase the aperture size.

12. A method as defined by claim 10 further defined by step (10) consisting in controllably impressing iden-. tical local indentations into the periphery of each enclosure to form corresponding bulges to the interior wall surface thereof and thereby decrease the internal volume of said enclosure in precise incremental steps, and step (15) comprising electropolishing the aperture edge surface of each septum to uniformly remove metal therefrom to controlled amounts and thereby precisely increase the aperture size.

13. A method of manufacturing multiple cavity Waveguides comprising the steps of providing a plurality of metallic cavity enclosures having open ends, providing a plurality of metallic septa conforming to said open ends and each including a central axial aperture, machining the length and outer periphery of said enclosures respectively identical within close tolerances, machining the interior dimensions of each of said enclosures to predetermined dimension commensurate with a predetermined operating frequency within close tolerances greater than said predetermined dimensions, machining the periphery of said septa to conform to the outer periphery of said enclosures within close tolerances, machining the dimensions of each of said septa apertures to predetermined dimensions commensurate with said operating resonant frequency within close tolerances less than said predetermined dimensions, annealing said enclosures and septa, honing the transverse faces of said enclosures and said septa flat and smooth, energizing each one of said enclosures with a variable radio frequency field simultaneously while observing the frequency response of said enclosure to determine the frequency at which peak response occurs, comparing the resonant frequencies so determined to said operating resonant frequency to determine deviations therefrom, repetitiously positioning a spherical surface adjacent the periphery of each of said enclosures, positioning a forming die adjacent the interior wall surface of said enclosure diametrically opposed to said spherical surface, applying pressure to said surface to impress same into the periphery of said enclosure, limiting the depth of penetration of said surface into said periphery, continuing the impressing process until sufficient bulges are formed at the interior wall surface of each enclosure to compensate said deviations from operating resonant frequency within close electrical tolerances, interposing each of said septa between identical resonant cavities having said operating resonant frequency, energizing said septum coupled cavities with a variable radio frequency field simultaneously while observing the frequency response of said cavities to determine the frequency at which peak response occurs, comparing the septa resonant frequencies so determined to said operating resonant frequency and determining deviations therefrom, electropolishing the aperture edge surface of each septum until an amount of metal is removed producing a change in the resonant frequency thereof compensatory to said deviation from operating resonant frequency, interposing each of said septa between a nonresonant cavity and a cavity resonant at said operating frequency, energizing said cavities with a variable radio frequency field while observing the response of said cavities to determine the frequency producing peak response, orienting said septum transversely upside down between said cavities and repeating the preceding step, marking the septum end face orientation producing peak response at greatest frequency, placing the cavity enclosures and said septa in alternate coaxial juxtaposition with the septa in similar marked end face orientation, axially clamping said enclosures and septa, contacting brazing alloy about each seam formed by abutting surfaces of said enclosures and septa, placing said clamped enclosures and septa in a reducing atmosphere and applying heat maintained at a temperature below the melting point of said alloy'to diffusion weld said abutting surfaces, the resulting diffusion welded seams porous to vacuum, raising the temperature of said heat to at least the melting point of said alloy to flow same around said welded surfaces and vacuum seal the welded seams, cooling said joined enclosures and septa, and removing the clamp means therefrom.

14. A method of manufacturing multiple resonant cavity waveguides comprising the steps of providing a length of metallic tubing, transversely cutting said tubing at equal axial increments to form a plurality of electrically conducting cavity rings, machining said cavity rings to identical dimensions within close tolerances, annealing said rings in a hydrogen atmosphere to remove stresses and strains therein, honing the end faces of said cavity rings flat and smooth, electrically testing each of said cavity rings to determine the resonant frequency thereof, comparing said resonant frequencies to a predetermined operating resonant frequency to determine deviations therefrom, electropolishing the interior wall surfaces of said cavity rings having resonant frequencies greater than said operating resonant frequency to tune same to said operating resonant frequency, electroplating the interior wall surfaces of said cavity rings having resonant frequencies less than said operating resonant frequency to tune same to said operating resonant frequency, providing a length of metallic bar stock having a cross section conforming to the outer cross section of said rings, cutting said bar stock at equal axial increments to form aplurality thin septa, drilling an axial aperture in each of said septa, machining said septa apertures to round the edges thereof, finish machining said septa to identical dimensions within close tolerances and in conformity to said machined cavity rings, annealing said septa in a hydrogen atmosphere to remove stresses and strains therein, honing the faces of said septa flat and smooth, electrically testing each of said septa to determine the resonant frequency thereof, comparing said resonant frequencies to said predetermined operating resonant frequency to determine deviations therefrom, electropolishing the round aperture edges of said septa having resonant frequencies less than said operating frequency to tune same to said operating resonant frequency, electroplating the rounded aperture edges of said septa having resonant frequencies greater than said operating frequency to tune same to said operating resonant fre- "quency, determining the axial direction of out-of-fiatness deformation of each septum, and assembling said cavity rings and said septa in alternate coaxial relation- "ship, said septa oriented in the same direction of deformation.

15. A method of manufacturing multiple resonant cavity waveguides comprising the steps of (1) providing a 'length of copper tubing, (2) transversely cutting said tubing at equal axial increments to form a plurality of electrically conducting cavity rings, (3) machining said cavity rings to identical dimensions within close tolerances, (4) annealing said rings in a hydrogen atmosphere -to remove all stresses and strains therein, (5) honing the "end faces of said cavity rings flat andsmooth, (6) clamping flat metallic plates at the end extremities of each ring to form a resonant cavity therewith, (7) energizing said cavity with a variable radio frequency field simultaneously while observing the response of said cavity to determine the frequency at which peak response occurs,

(8) comparing the cavity ring resonant frequencies so determined to a predetermined operating resonant frequency to determine deviations therefrom, (9) removing said metallic plates from the end extremities of said cavity rings, (10) Iepetitiousl y positioning a hard spher- 16 ical surface adjacent the periphery of each cavity ring determined to deviate below said operating frequency, (11) applying pressure to said surface to impress same into said periphery, (12) limiting the depth of penetration into said periphery by said surfaces whereby bulges are formed at the interior wall surfaces of said cavity rings, (13) forming said bulges to identity, (14) repeatin steps (10), (11), (12), (13) alternately with steps (6), (7), (8), (9) until the cavity ring is resonant at said operating frequency, (15) electropolishing the interior wall surface of each ring determined to deviate above said operating frequency, (16) repeating steps (6), (7), (8), (9) alternately with step (15) until the ring is resonant at said operating frequency, (17) providing a length of copper bar stock having a cross section conforming to the outer cross section of said cavity rings, (18) cutting said bar stock at equal axial increments to form a plurality of septa, (l9) drilling an axial iris aperture in each one of said septa, (20) machining said septa iris apertures to round the edges thereof, (21) finish machining said septa to identical dimensions within close tolerances and in conformity to the exterior cross section of said machined cavity rings, (22) annealing said septa in a hydrogen atmosphere to remove all stresses and strains therein, (23) honing the faces of said septa flat and smooth, (24) clamping each of said septa in interposition between a pair of like cavities resonant at said operating frequency, (25) energizing said septum coupled cavities with a variable radio frequency field simultaneously while observing the frequency response of said cavities to determine the frequency producing peak response, (26) comparing the septum resonant frequencies so determined to said operating resonant frequency to determine deviations therefrom, (27) removing said septa from said cavities, (28) electroplating and electropolishing the aperture edge surfaces of septa determined to deviate above and below said operating frequency respectively, (29) repeating steps (24), (25), (26), (27) alternately with step (28) until the resonant frequency of each septum is in agreement with said operating frequency, (29) clamping each of said septa in interposition between a non-resonant cavity and a cavity resonant at said operating resonant frequency, (30) energizing said septum coupled cavities with a variable radio frequency field simultaneously while observing the response of said cavities to determine the frequency producing peak response, (31) orienting each septum upside down between said cavities, (32) repeating step (30), (33) marking the septum end face orientation producing peak response at greatest frequency, (34) placing said cavity rings and said septa in alternate coaxial juxtaposition with the septa in similar marked end face orientation, (35) axially clamping said cavity rings and septa to establish intimate contact therebetween, (36) contacting silver solder wire, about each seam formed by abutting surfaces of said cavity rings and septa, (37) placing said clamped rings and septa in a reducing atmosphere and applying heat maintained at a temperature of between 450 C. to 600 C. below the melting point of said silver solder wire for several hours whereby diffusion occurs between said abutting surfaces and porous diffusion welded seams are produced therebetween, (38) raising the temperature of said heat to at least the melting temperature of said silver solder to flow same around said seams to establish pressure sealed diffusion welded joints, (39) cooling said cavity rings and septa, (40) and removing the clamp means therefrom.

16. A multiple cavity waveguide, comprising a plurality of metallic cavity enclosures having open ends, said enclosures having interiorly projecting self-supporting substantially hemispherical indentations of substantially equal size in respective quantities rendering their electrical equivalent volumes identical within tolerances of 1 part in 30,000, and a plurality of flat metallic septa conforming to the exterior cross-section of said enclosures 17 disposed in alternate coaxial succession therewith and secured to the open ends of adjacent ones thereof, said septa having iris apertures with electropolished surrounding edge surfaces, and apertures being electrically identical within tolerances of 1 part in 30,000.

17. Method of tuning oversized cavity rings comprising the following steps: placing a brinelling die at the interior wall surface of such a ring, placing an indenting punch corresponding to said die at a corresponding portion of the exterior wall surface of said ring, and pressing said punch radially inward into said exterior Wall surface, said punch having a restricting collar to limit depth of penetration.

18. Method of tuning oversized cavity rings comprising the following steps: placing a brinnelling die at the interior wall surface of such a ring, placing an indenting punch corresponding to said die at a corresponding portion of the exterior wall surface of said ring, pressing said punch radially inward into said exterior wall surface, said punch having a restricting collar to limit depth of penetration, and repeating said steps a predetermined number of times as calculated by dividing the total frequency deviation by the frequency change per indentation.

References Cited in the file of this patent UNITED STATES PATENTS 2,126,074 Wissler Aug. 9, 1938 2,195,314 Lincoln Mar. 26, 1940 2,228,087 Rose Jan. 7, 1941 2,382,549 Edmonson Aug. 14, 1945 2,567,701 Fiske Sept. 11, 1951 2,602,146 Ludi July 1, 1952 2,629,066 Eitel et a1 Feb. 17, 1953 2,629,774 Longacre Feb. 24, 1953 2,649,576 Lewis Aug. 18, 1953 2,662,277 Stone Dec. 15, 1953 2,725,353 Strobel Nov. 29, 1955 2,749,523 Dishal June 5, 1956 2,777,193 Albright et a1 Jan. 15, 1957 2,779,993 Pityo Feb. 5, 1957 2,787,766 Scheftelowitz Apr. 2, 1957 2,817,813 Rowen et a1. Dec. 24, 1957 2,824,289 Murdock Feb. 18, 1958 2,892,958 Nygard June 30, 1959 OTHER REFERENCES Hassell et al.: Electroforming Waveguide Components, Electronics, March 1946, pages 134-138. 

1. A METHOD OF PRODUCING A MULTIPLE CAVITY WAVEGUIDE COMPRISING THE STEPS OF (1) FORMING FROM ELECTRICALLY CONDUCTING MATERIAL A PLURALITY OF SIMILAR ENCLOSURES HAVING OPEN ENDS AND A PLURALITY OF FLAT SEPTA CONFORMING TO THE EXTERIOR CROSS SECTION OF SAID OPEN ENDS AND HAVING CENTRAL IRIS APERTURES THERETHROUGH, (2) ELECTRICALLY TESTING EACH OF SAID ENCLOSURES TO DETERMINE THE RESONANT FREQUENCY THEREOF, (3) COMPARING SAID RESONANT FREQUENCIES TO A PREDETERMINED OPERATING RESONANT FREQUENCY TO DETERMINE DEVIATIONS THEREFROM, (4) ALTERING THE INTERIOR VOLUME OF SAID ENCLOSURE AS REQUIRED TO PRODUCE RESONANCE THEREOF AT SAID OPERATING FREQUENCY, (5) REPEATING STEPS (2), (3), AND (4) ALTERNATELY UNTIL SAID ENCLOSURES RESONATE AT SAID OPERATING FREQUENCY, (6) ELECTRICALLY TESTING THE IRIS APERTURES OF EACH SEPTUM TO DETERMINE THE TRANSMISSIVE RESONANT FREQUENCY THEREOF, (7) COMPARING SAID TRANSMISSIVE RESONANT FREQUENCY TO SAID OPERATING FREQUENCY TO DETERMINE DEVIATIONS THEREFROM, (8) ALTERING THE SIZE OF SAID APERTURES AS REQUIRED TO PRODUCE RESONANCE THEREOF AT SAID OPERATING FREQUENCY, (9) REPEATING STEPS (6), (7), AND (8) ALTERNATELY UNTIL SAID SEPTA APERTURES RESONATE AT SAID OPERATING FREQUENCY, (10) DETERMINING THE AXIAL DIRECTION OF OUT-OF-FLATNESS DEFORMATION OF EACH ONE OF SAID SEPTA, AND (11) ASSEMBLING SAID ENCLOSURES AND SAID SEPTA ALL ORIENTED IN THE SAME DIRECTION OF OUT-OF-FLATNESS IN ALTERNATE COAXIAL RELATIONSHIP. 